A number of patents describe processes for the direct synthesis of pigments in a pigmentary form to avoid the additional expensive and oftentimes environmentally unfriendly pigment finishing processes (e.g. processes for particle size reduction and/or crystal-form modification). For example European Patent No. 643,110 and U.S. Pat. No. 5,424,429 describe a direct synthesis of quinacridone solid solutions and 2,9-dichloroquinacridone in pigmentary form, respectively, in the presence of quinacridone phthalimidomethyl derivatives. European Patent No. 685,530 describes the preparation of a direct synthesis of pigmentary grade dioxazine in the presence of a dioxazine derivative.
It is also known that sulfonic acid derivatives of certain pigments can effectively diminish the crystal growth during the isolation of the pigment from a reaction mixture. Such sulfonic acid derivatives are described, for example, in U.S. Pat. No. 3,386,843. Other patents describe the use of sulfonic acid derivatives of pigments to stabilize against recrystallization and change of crystal modification as, for example, in G.B. Patent No. 1,544,839 which is directed to phthalocyanine pigments.
U.S. Pat. No. 5,755,873 describes a method for the preparation of quinacridone pigments in which a quinacridone derivative is incorporated during synthesis and copending provisional application Ser. No. 60/087,773 describes a direct synthesis of pigmentary diketopyrrolopyrrole pigments in the presence of quinacridone or diketopyrrolopyrrole derivatives.
Although the addition of such known pigment derivatives can be advantageous, pigment synthesis in the presence of such derivatives in many cases does not provide the favored pigmentary crystal size, shape or crystal modification. Therefore many pigments so synthesized may still require finishing steps to obtain pigments with the preferred color characteristics.